Alloy for vacuum tube elements



I Patented Dec. 28,1937

human ALLOY FOR VIMJUUM TUBE ELEMENTS Ambrose J. Mandell, Westfleld, N. J.; Edward Mandel, administrator of said Mandell, deceased,

Ambrose 3.

assignor, by mesne assignments, to Radio Corporation of America, New York, N. 2., a corporation of Delaware No Drawing. Application November 20, 1926.

Serial No. 1936 149,801. Renewed September 3,

21 Claims. (cl. est-27.5)

My invention relates to vacuum tube devices and particularly to alloy metals for the construction of elements therein.

In the construction of vacuum tubes, such as electric lamps, rectifiers, triodes, etc., it is essential that conductormaterials be provided for a variety of portions of the device. In the case of electric lamps, seal wires and supporting wires are required. In the case of other vacuum'tubes such as rectifiers and triodes, there are a number of metal elements required, such as the anodes, cathodes and control electrodes as well as seal wires which carry current, and support wires which do not and the term element in this specification means these parts In all of these constructions, it is essential that the metals be free from occluded gases since the presence of gas in the device is harmful, or fatal to its opera-. tion. As the art progresses the requirements for such material in vacuum tubes are becoming progressively more and more severe, because of the necessity 'for handling larger and larger quantities of electricity at higher and higher voltagesand because of the resulting higher temperatures.

Among the qualities which are desirable in an alloy for such elements, the following may be mentioned:

1. The ability to withstand the erosive action 30 of an electron stream at high temperatures and at high voltages.

2. The ability to withstand deterioration, such as changes in crystal structure or internal structure under service conditions. of elevated temper- 35 atures. v

3. High thermal conductivity and high, or controlled electrical conductivity.

4. Resistance to oxidation at sealing temperatures. u

10 5. Sufllcient strength, toughness, and ductility to allow working into the finished form by ordinary methods.

6. The ability to be wet by molten glass in sealing. 1

Nickel has been used in the pastas a constituent of vacuum tubes, elements particularly in the form of rolled sheet for the anode structures and of wire forgrid structures, and the auxiliary supporting wires therein. Nickel alloys have also been used for certain purposes, particularly an alloy of nickel and iron covered with an adherent coating of copper to produce the well-known Dumetf seal wire. Pure nickel contains so much occluded gases that very elaborate heating and exhausting processes. are required to free the metal from gas sufliciently to permit its use in vacuum tubes in which it is desired that a high vacuum shall be maintained. The pure nickel has however a satisfactory electrical conductivity. The alloy of nickel and iron occludes 5 somewhat less gas, and when used as a seal wire, the occluded gas is of somewhat less importance.

I have discovered that by the addition of suitable proportions of silicon or of silicon and manganese or of silicon and other elements to nickel, an alloy may be produced which has one or more of the above mentioned desirable qualities and exhibits much greater suitability for vacuum tube elements than any previously known alloy. The alloy of my invention is resistant to oxidation, contains little occluded gas, is easily'worked by ordinary methods into the desired form, and may be made to have a co-efllcient of expansion closely similar to that of glass and to be wet by the glass.

Increased ability to withstand the eroding action of the electric discharge is conferred upon nickel by additions which increase the hardness and strength at high temperatures. Not all additions which produce this effect are suitable,

however, because many of them have a bad effect upon other properties, such as thermal and electrical conductivity, ductility, etc. Particularly, even small additions of silicon have a strengthening effect; and also greatly promote the resistance to oxidation and freedom from o'ccluded gases, and these effects are retained at high temperatures.

Additions of chromium and tungsten will likewise harden and strengthen nickel, but they have no effect on the gas content, and a much greater quantity of these meals is required to produce the same strengthening effect produced by a given quantity of, silicon, and the quantity which must be added may produce a serious lowering of the 40 thermal and electrical conductivity of the resulting alloy. This effect is so pronounced that the usefulness of these particular alloys is seriously limited.

Aluminum has an effect quite similar to silicon in strengthening nickel, promoting its resistance to oxidation and lowering the content of occluded gases. The accompanying bad effects are not so pronounced as they are for chromium or tungsten but are more pronounced than any produced by silicon. The efiects of zirconium are substantial, but the resistance to oxidation and the lowering of occlusion obtained by zirconium is not so good, and the high cost of zirconium is a serious disadvantage. Similar remarks apply to titanium and vanadium. Therefore. while small amounts of any or all oi these metals may be added to the alloy, the amounts added must not be excessive and will not serve to replace all of the silicon. ent, additions of some of these other metals may produce additional valuable properties.

Addition to the nickel of suflicient silicon or of silicon and the other metals mentioned, to produce the required resistance to erosion. to oxidation and to change of structure at high temperatures, will lower the ductility and toughness considerably, as compared to pure nickel. These latter qualities can be greatly improved and other desirable qualities imparted by the further addition to the alloy 01 a suitable proportion of manganese, without harm to-the previously mentioned desirable qualities, and this effect of the manganese is so valuable "that while manganese is not an absolutely essential constituent, the alloys containing it are insomerespects much superior to those free from it. -'.'.-;Too much manganese may be undesirable, however, as in excess it causes a lowering of the thermal and electrical conductivity. Inthe event that the material is used for filaments, this efiect may be highly desirable, and in the case oi such elements as anodes and grids, it is 01' minor consequence.

Metals such as copper and iron may under certain conditions have beneficial effects. They act to reduce both the thermal and electrical conductivity, which under certain conditions may be highly desirable. For instance, if the alloyis to be used for a filamentary cathode, the addition of copper may be used to bring the specific resistance of thematerial to-a pointwhich will be most suitable for the particular filament characteristics that are desired. This is particularly true of copper and to a lesser extent of iron. Iron on the other hand, has the somewhat objectionable property of reducing the resistance to oxidation, and if present in any substantial quantity, of tending towards brittleness.

The percentages of the various constituents of the alloy which have been found by experiment to be preferable and desirable are the following:

The greater portion of the alloy consists of nickel. Silicon should be present in amounts not less than V of 1% and not in excess of 6% to 7%. I With the silicon in the limiting value of 7% may be included all of the other elements except the manganese and the nickel, and cobalt. When manganese, which is of value in decreasing the content of the occluded gas, as well as in increasing the strength, toughness and conductivity of the alloys is included in the alloys it may be present in proportion as great as 10%, although 5% is usually sufllcient, and it should not be less than of 1%. Variation in the proportion of manganese will vary the electrical resistanceand' if a high resistance is required, as for filaments, small amounts of copper, chromium or tungsten may be added.

. Copper does not decrease the toughness or the ductility nor does it increase the absorption nor the occlusion of gas. It does increase the elec-= trical resistance without noticeable effect upon other properties of the alloy if not present in excess, and it is accordingly satisfactory to keep its proportion low.

Any or all of the elements, aluminum, zirconium, titanium and vanadium, may be used to replace a portion of the silicon. They may not be added in replacement of all the silicon, and ordi narlly will not be present in the alloy in percent-- If sufilcient silicon is however presages higher than 2%, although aluminum may be present up to 4%, or even 5%. Normally the silicon content should be not less than 40% of the metals added to the nickel or cobalt.

Alternatively, chromium and tungsten may be added in small proportions when t is desired to decrease the electrical conductivi They are 'without effect on the content of occluded gases,

and may have some strengthening efiect as well.

Small amounts of magnesium may be desirably added, which serves to reduce the gas content still further, and has no bad effects.

Iron is of benefit only when high electrical resistance is desired and under other conditions will be present only in such amounts as are unavoidable when working with commercial material.

The non -metallic elements or metalloids, such as sulphur, carbon, phosphorus, etc. should be kept as low as possible because of their bad eflfects on the mechanical properties of the alloy.

The bulk of the alloy should be nickel, although it is possible to substitute for the nickel, cobalt in any desired proportion without departing from the spirit of my invention, in using thev term nickel I shall consider cobalt to be the full equivalent thereof. Howeven-the high price of cobalt as compared to nickel makes it at the present time an undesirable substitute, and it oflers no substantial advantage over nickel, except when a high electrical resistance'is' desired and it is found undesirable to add suflicient copper. A substantial proportion of cobalt may then be added, which decreases the electrical and thermal conductivity without other change in properties of the alloy.

. It will be obvious that the specific instances, which have herein been described are intended solely in explanation of the nature of invention, and that vfurther various changes in the details thereof may be made in the details and proportions disclosed, by those skilled in the art without departing from the spirit of my invention, and it is desired therefore that only such limitations shall be imposed thereon as are required by the prior art or indicated in the appended claims.

I claim as my invention:--

1. An electrically conductive core for a thermionically active cathode comprising an alloy of nickel and silicon.

2. An electron-emitting cathode comprising a core composed of an alloy of a metal of the group containing nickel and up to 6% of silicon.

3. An electron emitting cathode for an electron discharge device comprising an alloy composed of a base selected from the group comprising nickel and cobalt and constituting at least 90% of the alloy, and an added quantity of substance taken from the. group comprising silicon, titanium, vanadium and zirconium, the added substance including at least silicon, and the silicon constituting at least /2 of 1% of the alloy.

- 4. An element for an electron discharge device composed of an alloy comprising a base selected from the group comprising nickel and cobalt and amass? constituting at least 90% of the alloy, and an added quantity of substance taken from the group including silicon, titanium, vanadium and zirconium, the added quantity including at least silicon and vanadium, the silicon constituting at least of 1% of the alloy, and vanadium constituting at least /4 of 1% of the alloy.

6. An element for an electron discharge device composed of an alloy comprising a base selected from the group comprising nickel and cobalt and constituting at least 90% of the alloy, and an added quantity of substance taken from the group including silicon, titanium, vanadium and zirconium, the added quantity including at least silicon and zirconium, the silicon constituting at least of 1% of the alloy, and zirconium constituting at least l of 1% of the alloy.

'7. In a hermetically sealed evacuated tube, metallic elements exposedto the rarefied atmosphere within said tube and composed of a malleable and ductile deoxidized and degasified alloy comprising a metal having the characteristics common to nickel andcobalt and containing approximately 1% silicon, and low in carbon.

8. A cathode for an electron discharge device composed of an alloy comprising a base selected from the group comprising nickel and cobalt and constituting at least 90% .of the alloy, and an,

added quantity of silicon, the silicon constituting at least of 1% of the alloy.

9. A cathode element for an electron discharge device. composed of an alloy comprising a base selected'from the groupcomprising nickel and cobalt and constituting at least 90% of the alloy, and an added quantity of substance taken from the group comprising silicon, titanium, vanadium and-zirconium, the added quantity including at least silicon and titanium, the silicon constitutingfat least of 1% of the alloy, and the titanium constituting at least 1 of 1% of the alloy.

10. A cathode element for an electron discharge device composed of an alloy comprising a base selected from the group comprising nickel and cobalt and constituting at least 90% of the alloy, and an added quantity of substance taken from the group including silicon, titanium, vanadium and zirconium,'the added quantity including at least silicon and vanadium, the silicon constituting at least A, of 1% of the alloy, and vanadium constituting at least of 1% oi. the alloy.

11. In a hermetically sealed evacuated tube, a metallic cathode element exposed to the rarefied atmosphere within said tube and composed of a malleable and ductile deoxidized and degasifled alloy comprising a metal having the characteristics common to nickel and cobalt and containing from /3 of 1% to 7% of silicon, and low in carbon.

12. In a hermetically sealed evacuated tube, a. metallic cathode element exposed to the rarefied atmosphere within said tube and composed of a malleable and ductile alloy. comprising a metal having the characteristics common to nickel and cobalt and containing a deoxidizer in excess of the amount required to effect substantial deoxidation so as to efiectalso substantial degasification of the alloy, the unoxidized excess remaining in the alloy as a constituent thereof, said alloy being low in carbon.

13. In a hermetically sealed evacuated tube, a metallic cathode element exposed to the rarefled atmosphere within said tube and composed of a malleable and ductile alloy comprising a metal having the characteristics common to nickel and cobalt'and containing silicon in excess of the amount required to eflect substantial deoxidation so as to efiect also substantial degasiflcation of the alloy, the unoxidized excess of the silicon remaining in the alloy as a constituent thereof, said alloy being low in carbon.

it. An electron emitting cathode for electron discharge devices comprising a core composed of an alloy consisting of 1% to 3% of silicon, to 1% of titanium, and the remainder of metal selected from the group comprising nickel and cobalt.

15. An electron emitting cathode for electron discharge devices comprising an alloy composed of a base selected from the group comprising nickel and cobalt and constituting at least 90% of the alloy, and added metals consisting of silicon and titanium, the silicon constituting at least of 1% of the alloy and also at least 40% of the added metals.

16. An electron emitting cathode for electron discharge devices comprising an alloy composed of a base selected from the group comprising nickel ,and cobalt and constituting at least 90% of the alloy, and added metals selected from the group including silicon, titanium and iron, the silicon constituting at least of 1% oi the alloy, and also at least 40% of the added metals, and the titanium constituting at least of 1%of the alloy.

17. An electron emitting cathode for electron discharge devices comprising an alloy composed of a base selected from the group comprising nickel and cobalt and constituting at least 90% of the alloy, and added metals consisting of iron and titanium, the titanium constituting at least of 1% of the alloy.

18. An element for an electron discharge device comprising an alloy consisting of a base selected from the group comprising nickel and cobalt and constituting at least 93% of the alloy and of added metals including at least silicon and aluminum, the silicon constituting from V; to 3% of the alloy and the aluminum constituting up to 4% of the alloy.

19. A cathode element for an electron discharge device comprising a base selected from the group comprising nickel and cobalt and constituting at least 90% of the alloy and. an added quantity of metal taken from the group comprising silicon, aluminum and titanium, the added metals including at least silicon and aluminum, the silicon constituting at least of the alloy and the aluminum constituting at least A,% of the alloy.

20. An electron emitting cathode for electron discharge devices comprising an alloy composed of a base selected from a group comprising nickel and cobalt and constituting at least 95% of the alloy and of added metals consisting of silicon and aluminum, the silicon constituting from to 3% of the alloy and the aluminum constituting substantially 2% of the alloy.

21. A metallic cathode element for electron discharge devices composed of a malleable and ductile alloy low in carbon and consisting of a base selected from a group comprising nickel and cobalt and constituting at least 90% of the alloy, aluminum constituting up to 4% of the alloy, said alloy containing a deoxidizer in excess of the amount required to effect substantial deoxidation and substantial degasiflcation of the alloy, the unoxidized excess remaining in the alloy as a constituent thereof.

AMBROSE J. MANDELL.

DISOLAlMER 2,103,267.-Anrbros J. Mandell, 'We stfield, N. J. ALLOY FOR VACUUM TUBE" ELEMENTS. Patent dated December 28, 1937. Disclaimer filed June 11, I 1938, by the assignee, Radio Gorpomtion of America. Hereb enters this disclaimer of claims 9, 10, 12, and 13 of said Letters Patent.

[ flicial Gazette July 5, 1938.] F 

